1. Field of the Invention
The present invention relates to a power amplifier for use in wireless devices such as mobile terminals.
2. Background Art
Power amplifiers typically have a function to switch between two or more power amplification paths therein so as to achieve high power load efficiency over the entire power range. A high frequency switch is inserted in series with the output side of each power amplification path in order to isolate the transistors in one path from those in other paths and thereby prevent each transistor from being subjected to unwanted voltages when the transistor is turned off.
Further, some power amplifiers are configured such a manner that a high frequency switch is connected between the output side of one of the power amplification paths and ground (a shunt configuration), and that power amplification path is fully short-circuited to ground by the high frequency switch when the high frequency switch is turned on, thereby controlling the impedance of the power amplification path (see, e.g., Japanese Laid-Open Patent Publication No. 2002-185270).